Green Synthesis and Characterization of Zinc Oxide Nanoparticles via Thyme for Biomedical Applications: Effect of Plant Extract Concentration and Drying Method

Abstract

Green synthesis of nano particles using plant extracts is sustainable, cost-effective, and eco-friendly. However, the synthesis parameters are still being investigated. In this study, zinc oxide nanoparticles (ZnO NPs) were prepared via thyme extract (green synthesis) and the effect of synthesis parameters were investigated. Samples with different concentrations of thyme plant extract (PE) (10, 16 & 24% (v/v) PE / Zn salt solution) were prepared and two different drying methods (freeze-drying (FD) and oven-drying (OD)) were performed. XRD results showed the hexagonal crystalline ZnO were formed with considerable crystallinity (70.8-75.1%) without further heat treatment (calcination). The crystallite sizes of ZnO NPs were determined to be in the range of 11.9-14.8 nm. The ZnO NPs prepared via PE concentration of 16% (v/v) and freeze-drying was with the finest crystallite size (11.9 nm) and considerable crystallinity (72.9%). ZnO NPs prepared via FD method were found to have smaller particle sizes, thus providing a higher surface-to-volume ratio. DLS (dynamic light scattering) analysis was used for determining the particle size distribution (PSD) and surface charge of ZnO NPs at acidic, neutral and basic pH values. The antibacterial characteristics of ZnO NPs were determined against Gram (+) and (-) bacteria. The ZnO NPs with the finest microstructure (16% PE (v/v), FD) had the highest antibacterial activity. The green synthesized ZnO NPs prepared in this study may be promising candidates for various applications including biomaterials and biomedical applications with their fine microstructure and considerable antibacterial activity.